Depth of field with transparent object

This is what i know. Unity build-in DepthOfField34 image effect use depth map to make the depth of field effect. However transparent shader doesn't write in Z-buffer, which makes the effect incorrect. The easy way is to write a customised transparent shader that write sin Z-buffer.

But...

now I want to make several transparent objects overlap on screen.The upper solution doesn't work in this case. Is there any method to do this?